1. Technical Field
The present invention relates to an image processing device used for a digital camera equipped with a color image capturing device, such as a CCD or a CMOS, and more particularly to an image processing method, an image processing device, a semiconductor device, an electronic apparatus, an image processing program, and a computer-readable storage medium, capable of removing pseudo colors generated by a color interpolation process.
2. Related Art
In general, digital cameras, such as digital video cameras and digital still cameras, are mainly classified into a three-chip digital camera using three image capturing sensors, such as CCDs (Charge Coupled Devices) and CMOSs (Complementary Metal Oxide Semiconductors), and a single-chip digital camera using only one image capturing sensor.
In the three-chip digital camera, incident light is divided into the three primary colors of red (R), green (G), and blue (B) by dichroic mirrors, and the divided color components are respectively converted into R, G, and B digital images by three image capturing sensors. Therefore, since the three-chip digital camera has a complicated optical system structure, but can obtain high-resolution images, the three-chip type is generally used for digital video cameras for business purposes and high-quality digital camera.
On the other hand, the single-chip digital camera has color filters in which R, G, and B color pixels are arranged on one image capturing sensor in a block shape, and converts light information passing through color filters corresponding to each pixel into digital data. Therefore, the single-chip digital camera has resolution lower then that of the three-chip digital camera, but has a small size, a light weight, low power consumption, and a low manufacturing cost, compared to the three-chip digital camera. Therefore, the single-chip type is mainly used for consumer digital video cameras and digital still cameras.
Further, in recent years, the consumer color video cameras using the three-chip type have been produced. In addition, a two-chip type digital camera using two image capturing sensors has been proposed, and the two-chip type has an intermediate character between these two types, but it has not been used in recent years. The single-chip digital camera requires a color interpolation process for forecast-interpolating lost color components. However, since the color interpolation process, which will be described in detail, is to create color data that does not exist in a target pixel from values of pixels around the target pixel by a supposing method, it is difficult to exactly calculate pixel values at a portion of an image, such as an edge portion, in which a pixel value is suddenly changed. Therefore, an image having a color balance different from a conventional color balance occurs in the edge portion in which an exact pixel value is not obtained, and the image appears to be a pseudo color, which causes an unclear image or the deterioration of image quality.
Therefore, in the conventional arts, as described in Japanese Unexamined Patent Application Publication No. 2003-244711, RGB data obtained by a simple color interpolation process is converted into a brightness signal Y and a color-difference signal C, and a high-pass enhancement filtering process or a low-pass enhancement filtering process is performed on the respective signals to improve image characteristics.
Meanwhile, Japanese Unexamined Patent Application Publication No. 2002-10280 and 2001-231052 disclose a color interpolating method capable of preventing the lowering of image quality, such as the generation of a pseudo color and an unclear image, by adaptively performing color interpolation using wide-area image data.
Further, in a method of Japanese Unexamined Patent Application Publication No. 2003-244711 out of the conventional arts, a transformation formula for converting the RGB data obtained by the color interpolation process into the brightness signal Y and the color-difference signal C is fixed. Therefore, when a value of a specific color in a pixel unit to be process (for example, a pixel unit having 2 rows by 2 columns of pixels or a pixel unit having 3 rows by 3 columns of pixels) is large at the time of simple color interpolation, the overall resolution of an image is greatly affected by the resolution of the color having a large value, which results in the lowering of the overall resolution.
For example, in the case in which the color interpolation process is performed in a pixel unit having 2 rows by 2 columns of pixels composed of an R pixel, a B pixel, and two G pixels, when a value of the R pixel is extremely large, the color interpolation process is performed under the influence of the R pixel (or the B pixel), so that an image is generated with the resolution of the R pixel. As a result, an image is displayed with lower resolution corresponding to half the resolution obtained by the conventional sensor.
Meanwhile, Japanese Unexamined Patent Application Publication No. 2001-231052 requires a plurality of line memories since it performs the color interpolation process using wide-area image data and needs to perform the process with complicated calculation. Therefore, there is a problem in that a processing load may increase as a whole. In addition, in an RGB mosaic arrangement, color interpolation is performed on G using the correlation between pixels, and a pixel to be used is determined using the correlation of G data with respect to R and B. Therefore, when a switching point of processing is frequently generated at an edge portion of an image, it is difficult to reproduce a smooth edge.
Further, in both conventional techniques, a specific color is exactly calculated, and then the other colors are calculated. Therefore, an additional calculation process for the other colors is needed, which causes an increase in processing load.
Accordingly, the present invention is designed to solve the above-mentioned problems, and it is an object of the present invention to provide an image processing method, an image processing device, a semiconductor device, an electronic apparatus, an image processing program and a computer-readable storage medium, capable of reducing an image processing load, of preventing the lowering of resolution, and of reliably reproducing a smooth and natural edge of an image.